Portable power supplies have become an increasingly important part of our society. Examples of where portable power supplies are needed include portable computers, cellular communication devices and video games.
Power supplies for portable devices are typically constructed from silicon semiconductors (e.g., silicon diodes). The pervasive use of silicon diodes, in no small part, is because of the inexpensive manner in which such devices can be fabricated.
While silicon diodes are inexpensive, they also suffer from a number of disadvantages. One of the biggest disadvantages is electrical noise. Silicon diodes, in fact, typically require the use of noise suppression (snubber) circuitry. However, the use of snubber circuitry results in a considerable increase in the size and weight of power supplies. Another disadvantage is the efficiency of the circuit, especially at high frequency, because of switching losses due to high reverse recovery times in the silicon devices.
Alternate materials, such as silicon carbide (SiC), have been proposed. The publicly available CREE Application Note No. CPWR-AN01 Rev, available from Cree, Inc. 4600 Silicon Dr., Durham, N.C. 27703 (Copyright 2002), asserts that SiC diodes could significantly reduce electrical noise and would be expected to eliminate the need for snubber circuits in some power supplies.
However, there are significant disadvantages to the use of SiC. One of the chief disadvantages of the use of SiC is cost. The relatively high cost makes the construction of power supplies with SiC diodes commercially unacceptable.
On the one hand, the use of SiC diodes in portable power supplies makes those power supplies smaller and lighter. On the other hand, the use of Si PiN diodes makes a power supply too heavy and may run hotter.
In addition, where SiC diodes have been described, their use has been limited. For example, U.S. Pat. No. 6,657,874 to Yu describes a voltage inverter that uses SiC diodes for reverse blocking of switching elements. Yu Differs from the subject matter of the invention in that Yu is directed to the generation of an AC output. Yu also differs in that the switching elements of the Yu inverter operate at a relatively low frequency (e.g., 60 Hz versus several kHz for the switching elements of power supplies providing a DC output).
One alternative material for making diodes that has not been generally recognized is gallium-nitride (GaN). However, prior uses of GaN has been limited to light emitting diodes (LEDs). Because of the importance of portable devices, a need exists for power supplies as small and light as those using SiC, but a cheap as those using Si PiN diodes.